[PATCH] hwmon: (adm1275): Add device tree param for shunt resistor

[Kun Yi]

Thanks. I changed the documentation piece and submitted v2.

On Fri, Sep 28, 2018 at 11:30 AM Guenter Roeck <linux at roeck-us.net> wrote:

> On Fri, Sep 28, 2018 at 10:45:00AM -0700, Kun Yi wrote:
> > The ADM series of hotswap controllers support extending
> > the current measurement range by using a sensing resistor
> > value other than the typical 1 mOhm. For example, using a 0.5 mOhm
> > sensing resistor doubles the maximal current can be measured.
> >
> > Current driver assumes a shunt resistor value of 1 mOhm in calculation,
> > meaning for other resistor values, hwmon will report scaled
> > current/power measurements. This patch adds a device tree parameter so
> > that individual boards can configure its shunt resistor value.
> >
> Please copy DT maintainers for all DT changes.
>
> > Signed-off-by: Kun Yi <kunyi at google.com>
> > ---
> >  .../devicetree/bindings/hwmon/adm1275.txt     | 19 +++++++++++++++++++
> >  Documentation/hwmon/adm1275                   |  3 +++
> >  drivers/hwmon/pmbus/adm1275.c                 | 15 +++++++++++++--
> >  3 files changed, 35 insertions(+), 2 deletions(-)
> >  create mode 100644 Documentation/devicetree/bindings/hwmon/adm1275.txt
> >
> > diff --git a/Documentation/devicetree/bindings/hwmon/adm1275.txt
> b/Documentation/devicetree/bindings/hwmon/adm1275.txt
> > new file mode 100644
> > index 000000000000..a182fa195ed1
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/hwmon/adm1275.txt
> > @@ -0,0 +1,19 @@
> > +adm1275 properties
> > +
> > +Required properties:
> > +- compatible: Must be one of the supported compatible strings in
> > +  Documentation/hwmon/adm1275
>
> It would be more appropriate to list those here as devicetree properties.
> The information in Documentation/hwmon/adm1275 does not include the "adi,"
> prefix.
>
> Thanks,
> Guenter
>
> > +- reg: I2C address
> > +
> > +Optional properties:
> > +
> > +- shunt-resistor-micro-ohms
> > +     Shunt resistor value in micro-Ohm
> > +
> > +Example:
> > +
> > +adm1272 at 10 {
> > +     compatible = "adi,adm1272";
> > +     reg = <0x10>;
> > +     shunt-resistor-micro-ohms = <500>;
> > +};
> > diff --git a/Documentation/hwmon/adm1275 b/Documentation/hwmon/adm1275
> > index 39033538eb03..5e277b0d91ce 100644
> > --- a/Documentation/hwmon/adm1275
> > +++ b/Documentation/hwmon/adm1275
> > @@ -58,6 +58,9 @@ The ADM1075, unlike many other PMBus devices, does not
> support internal voltage
> >  or current scaling. Reported voltages, currents, and power are raw
> measurements,
> >  and will typically have to be scaled.
> >
> > +The shunt value in micro-ohms can be set via device tree at
> compile-time. Please
> > +refer to the Documentation/devicetree/bindings/hwmon/adm1275.txt for
> bindings
> > +if the device tree is used.
> >
> >  Platform data support
> >  ---------------------
> > diff --git a/drivers/hwmon/pmbus/adm1275.c
> b/drivers/hwmon/pmbus/adm1275.c
> > index 13600fa79e7f..f569372c9204 100644
> > --- a/drivers/hwmon/pmbus/adm1275.c
> > +++ b/drivers/hwmon/pmbus/adm1275.c
> > @@ -373,6 +373,7 @@ static int adm1275_probe(struct i2c_client *client,
> >       const struct coefficients *coefficients;
> >       int vindex = -1, voindex = -1, cindex = -1, pindex = -1;
> >       int tindex = -1;
> > +     u32 shunt;
> >
> >       if (!i2c_check_functionality(client->adapter,
> >                                    I2C_FUNC_SMBUS_READ_BYTE_DATA
> > @@ -421,6 +422,13 @@ static int adm1275_probe(struct i2c_client *client,
> >       if (!data)
> >               return -ENOMEM;
> >
> > +     if (of_property_read_u32(client->dev.of_node,
> > +                              "shunt-resistor-micro-ohms", &shunt))
> > +             shunt = 1000; /* 1 mOhm if not set via DT */
> > +
> > +     if (shunt == 0)
> > +             return -EINVAL;
> > +
> >       data->id = mid->driver_data;
> >
> >       info = &data->info;
> > @@ -654,12 +662,15 @@ static int adm1275_probe(struct i2c_client *client,
> >               info->R[PSC_VOLTAGE_OUT] = coefficients[voindex].R;
> >       }
> >       if (cindex >= 0) {
> > -             info->m[PSC_CURRENT_OUT] = coefficients[cindex].m;
> > +             /* Scale current with sense resistor value */
> > +             info->m[PSC_CURRENT_OUT] =
> > +                     coefficients[cindex].m * shunt / 1000;
> >               info->b[PSC_CURRENT_OUT] = coefficients[cindex].b;
> >               info->R[PSC_CURRENT_OUT] = coefficients[cindex].R;
> >       }
> >       if (pindex >= 0) {
> > -             info->m[PSC_POWER] = coefficients[pindex].m;
> > +             info->m[PSC_POWER] =
> > +                     coefficients[pindex].m * shunt / 1000;
> >               info->b[PSC_POWER] = coefficients[pindex].b;
> >               info->R[PSC_POWER] = coefficients[pindex].R;
> >       }
> > --
> > 2.19.0.605.g01d371f741-goog
> >
>


-- 
Regards,
Kun
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